1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus to be used in a chemical vapor deposition (CVD) process employed in manufacturing semi-conductor devices or electronic components, especially to the CVD apparatus of the vertical load lock, reduced-pressure type.
2. Description of the Related Art
Recent trends of high integration and microscopic configuration of semiconductors has resulted in the increase of wafer diameter to as large as 5 inches, 6 inches, and even 8 inches. And it is well-known that, in recent years, polycrystalline silicon film, silicon nitride film or silicon oxide film which are made by chemical vapor deposition (CVD) have played an important role as conductive film, or insulating films for the semiconductors and small electronic components. Especially, in a batch type CVD apparatus using a diffusion furnace which has a high through-put, in order to correspond to the increase of wafer diameter and automation of manufacturing, the CVD processing apparatus changes from the horizontal type to the vertical type. Furthermore, load lock configuration is adopted to prevent thermal oxidation of the silicon wafer by oxygen in the air before CVD processing and to decrease undesirable growth of flakes and dust on the inside wall of the reaction chamber.
The conventional CVD apparatus generally comprises a reaction chamber, which has a boat holder for containing a boat which can hold a number of semiconductor wafers or substrates mounted rotatably on an elevator, a reaction gas injecting port connected to a reaction gas source, an evacuation port connected to a vacuum pump and a heater for heating the reaction chamber and the wafers therein, a loading chamber which is connected to the reaction chamber with a gas-tight gate-valve, and an unloading chamber which is connected to the reaction chamber with another gas-tight gate-valve.
The wafers or substrates to be CVD-treated are first loaded into the loading chamber, and then by temporarily opening the first gas-tight gate-valve, the object wafers or substrates are loaded into the boat in the heated reaction chamber. After completion of the CVD reaction, deposited wafers or substrates are removed from the boat of the reaction chamber to the unloading chamber by temporarily opening the second gas-tight gate-valve.
In the above-mentioned conventional CVD apparatus, the loading chamber and the unloading chamber are connected to evacuation means (i.e., vacuum pumps) through respective valves. The reaction chamber is filled with reaction gas after loading the wafers or substrates therein and closing the gas-tight gate-valves and subsequent evacuation occurs through the evacuation port thereof.
The above-mentioned conventional CVD apparatus has the following problem. The reaction gas entering the reaction chamber is likely to diffuse into the buffer chamber which has a relatively lower pressure than the reaction chamber and to form undesirable deposition of film on various parts in the buffer chamber, such as the boat or wafer holding shelves in the buffer chamber. The deposited film is likely to peel off and make undesirable flakes or dust on the wafers or substrates, thereby inducing defects in the products.